1. Field of the Invention
The present invention relates to a compact meander antenna that can be used, for example, in a mobile communication terminal or a local area network (LAN), and to a method for tuning its resonance frequency.
2. Description of the Related Art
Antennas in conventional mobile communication terminals are generally of a type in which a whip antenna 21 is attached to a casing 22 of a communication terminal, as illustrated for example in the perspective view of FIG. 6.
In recent years, progress in mobile communications and the diversification of services has led to the spread of portable terminals and, in view of portability, to communication terminals with more compact casings. Accordingly, components that are integrated or attached are becoming smaller and lighter. However, since the conventional whip antenna 21 protrudes from the casing 22, a more compact design in which also the antenna does not protrude from the casing is desirable in order to make the terminal even more compact. Also a lighter weight is desirable.
In order to fulfill this need, meander antennas having, as a compact antenna, a radiation electrode made of a meandering conductor have been developed.
For example, FIG. 7 is a perspective view of a chip antenna disclosed in Japanese Unexamined Patent Publication JP-A 9-55618 (1997). In this chip antenna, a meandering conductor 13 is provided on an upper side of a substrate 11. The meandering conductor 13 is connected by a feed terminal 17 to a contact portion of a terminal electrode 12 provided on a lateral side of a substrate 11. Thus, the antenna can be made more compact by providing the conductor 13 serving as the radiation electrode with a meandering shape.
It is known that in this meander antenna, as in a xcex/4 (quarter wavelength) monopole antenna, the resonance frequency depends on the ground size of the base to which the substrate is attached. Consequently, it is necessary to design the pattern, that is, shape and dimensions of the conductor, such that the desired resonance frequency is attained, in accordance with the ground size of the base.
However, there is a problem that in meander antennas that have been made compact by making the conductor meandering, the resonance frequency tends to vary due to increased capacitance and electric coupling between the conductor lines, and due to the dielectric constant of the substrate, for example.
In order to solve these problems, it is an object of the invention to provide a compact meander antenna whose resonance frequency can be tuned easily, and with which adaptation to ground bases of various sizes is possible, while it is possible to adjust variations of the resonance frequency occurring due to manufacturing variations to a level that is usable with respect to the target resonance frequency, as well as to provide a method for tuning the resonance frequency of such a meander antenna.
As a result of intense studies into conductor patterns for meander antennas, the inventors of the invention found that these objects can be achieved as described below, and thus conceived of the invention.
The invention provides a meander antenna comprising:
a meandering conductor that is formed on a surface of a substrate made of a dielectric material or a magnetic material; and
a short-circuit conductor line that forms a short-circuit between two parallel opposing lines into which the conductor is bent, or an open conductor line for short-circuiting the two parallel opposing lines. a meander antenna which includes a meandering conductor that
Also the invention provides a meander antenna comprising:
a meandering conductor that is formed inside a substrate made of a dielectric material or a magnetic material; and
a short-circuit conductor line that forms a short-circuit between two parallel opposing lines into which the conductor is bent, or an open conductor line for short-circuiting the two parallel opposing lines,
wherein the substrate is provided with a window portion at which the short-circuit conductor line and the open conductor line are exposed.
In the invention it is preferable that a plurality of short-circuit conductor lines or open conductor lines are provided between the two parallel opposing lines.
In the invention it is preferable that the short-circuit conductor lines or open conductor lines are arranged at a spacing that is within 2% of a total length of the meandering conductor.
The invention provides a method for tuning resonance frequency of the above-described meander antenna, comprising cutting open the short-circuit conductor line, or short-circuiting the open conductor line.
The invention provides a method for tuning resonance frequency of the above-described meander antenna, comprising successively cutting open the plurality of short-circuit conductor lines starting at the open side of the two lines, or successively short-circuiting the plurality of open conductor lines starting at the short-circuit side of the two lines.
In the invention it is preferable that, when f is the target resonance frequency, fxe2x80x2 is the resonance frequency before tuning, a is a pattern length of the conductor short-circuited by the short-circuit conductor lines, and x is the tuning length of the pattern length necessary to obtain the target resonance frequency f after tuning, then the short-circuit conductor lines are cut open such that the tuning length best approximates the tuning length x derived from the equation x=(fxe2x80x2/fxe2x88x921)a.
In the invention it is preferable that, when f is the target resonance frequency, fxe2x80x2 is the resonance frequency before tuning, b is a pattern length of the conductor before short-circuiting open conductor lines, and y is the tuning length of the pattern length necessary to obtain the target resonance frequency f after tuning, then the open conductor lines are short-circuited such that the tuning length best approximates the tuning length y derived from the equation y=(1xe2x88x92fxe2x80x2/f)b.
In the invention it is preferable that the short-circuit conductor lines are arranged on the short-circuit side of the two parallel opposing lines, and the open conductor lines are arranged on the open side of the two parallel opposing lines.
The invention provides a method for tuning the resonance frequency of the above-described meander antenna, comprising cutting open the short-circuit conductor lines, or short-circuiting the open conductor lines.
In the invention, it is preferable that relative dielectric constant xcex5r of the dielectric material is 3 to 120, or magnetic permeability xcexc of the magnetic material is 1 to 8.
According to the invention, a meander antenna is provided with a short-circuit conductor line that forms a short-circuit between two parallel opposing lines into which a meandering conductor formed on a substrate has been bent, or an open conductor line for short-circuiting the two parallel opposing lines is open. Consequently, when an antenna has been manufactured in which the resonance frequency is higher than the target resonance frequency, then the resonance frequency can be tuned and lowered by extending the pattern length of the meandering conductor by cutting open the short-circuit conductor line. Or, when an antenna has been manufactured in which the resonance frequency is lower than the target resonance frequency, then the resonance frequency can be tuned and increased by shortening the pattern length of the meandering conductor by short-circuiting the open conductor line. As a result, the resonance frequency of a compact meander antenna can be tuned easily, and adaptation to ground bases of various sizes is possible, while it is possible to adjust variations of the resonance frequency occurring due to manufacturing variations to a level that is usable with respect to the target resonance frequency.
Furthermore, if a plurality of short-circuit conductor lines or open conductor lines are formed between the two parallel opposing lines, then it is possible to tune and gradually increase or decrease the resonance frequency by successively cutting them open or short-circuiting them. If the short-circuit conductor lines and the open conductor lines are arranged at a spacing that is within 2% of the total length of the meandering conductor, then a tuned resonance frequency can be achieved that is kept within 4% of the target resonance frequency, and the resonance frequency can be tuned to a level that poses no problem in practice.
Furthermore, it is possible to approximate the target resonance frequency by gradually decreasing or increasing the resonance frequency by successively cutting open the short-circuit conductor lines starting at the open side of the two parallel opposed lines if a plurality of short-circuit conductor lines are cut open, or by successively short-circuiting the open conductor lines starting at the short-circuit side of the two parallel opposed lines if a plurality of open conductor lines are short-circuited. Furthermore, when f is the target resonance frequency, fxe2x80x2 is the resonance frequency before tuning, a is a pattern length of the conductor short-circuited by the short-circuit conductor lines, and x is the tuning length of the pattern length necessary to obtain the target resonance frequency f after tuning, then it is possible to tune the resonance frequency efficiently such that the resonance frequency is kept for example within xc2x12% of the target resonance frequency f by cutting the short-circuit conductor lines open such that the tuning length best approximates the tuning length x derived from the equation x=(fxe2x80x2/fxe2x88x921)a. Or, when f is the target resonance frequency, fxe2x80x2 is the resonance frequency before tuning, b is a pattern length of the conductor before short-circuiting open conductor lines, and y is the tuning length of the pattern length necessary to obtain the target resonance frequency f, then it is possible to tune the resonance frequency efficiently such that the resonance frequency is kept for example within xc2x12% of the target resonance frequency f by short-circuiting the open conductor lines such that the tuning length best approximates the tuning length y derived from the equation y=(1xe2x88x92fxe2x80x2/f)b.
Furthermore, it is possible to tune and increase or decrease the resonance frequency by arranging the short-circuit conductor lines on the short-circuit side of the two parallel opposing lines and the open conductor lines on the open side of the two parallel opposing lines, and cutting open the short-circuit conductor lines or short-circuiting the open conductor lines, thus making it possible to efficiently tune to the target resonance frequency.
The invention provides a compact meander antenna whose resonance frequency can be tuned easily, and with which adaptation to ground bases of various sizes is possible, while it is possible to adjust variations of the resonance frequency occurring due to manufacturing variations to a level that is usable with respect to the target resonance frequency, as well as a method for tuning the resonance frequency of such a meander antenna.